1. Field of the Invention
This invention relates to a novel vanadium-phosphorus oxide possessing a specific X-ray diffraction pattern, a method for the production of the oxide, a catalyst for vapor phase oxidation formed of the oxide, and a method for partial vapor phase oxidation of a hydrocarbon.
2. Description of the Prior Art
Various studies have been being continued concerning vanadium-phosphorus oxides and researches on the physical properties of these oxides and on the development of uses therefor have been under way at the same time. Particularly, it is well known that vanadium-phosphorus oxides are effective in the production of maleic anhydride by the vapor phase oxidation of such hydrocarbons as butane, butene, and butadiene which have four carbon atoms (C4 hydrocarbons). It is also well known that the catalytically effective component of a vanadium-phosphorus oxide is divanadyl pyrophosphate, a crystalline oxide having the composition of (VO).sub.2 P.sub.2 O.sub.7. This divanadyl pyrophosphate is obtained by synthesizing vanadyl hydrogen orthophosphate (VOHPO.sub.4.0.5 H.sub.2 O), the precursory thereof, calcining the precursor, and further subjecting the calcined precursor to a so-called activating treatment by a calcination in the current of an inactive gas or the mixed gas of a hydrocarbon gas such as butane with air thereby effecting topotactic rearrangement of the precursor.
It is well known that maleic anhydride is obtained by subjecting n-butane, 1-butene, 2-butene, butadiene, or a mixture thereof (hereinafter referred to collectively as "C4 hydrocarbon") to a vapor phase oxidation in the presence of a vanadium-phosphorus oxide catalyst. Many improved vanadium-phosphorus oxide catalysts and methods for the production thereof have been already proposed.
Some of these improved vanadium-phosphorus oxide catalyst have been specified by methods of their preparations and others have been specified by patterns of their X-ray diffraction peaks (JP-A-53-61,588, JP-A-56-41,816, JP-A-56-45,815, JP-A-59-132,938, and JP-A-05-15,781). It is held that in the vanadium-phosphorus oxide catalysts, those having vanadium in a state approximating closely to tetravalence are more favorable for the production of maleic anhydride than those having vanadium in a state approximating closely to pentavalence (JP-A-50-35,088 and JP-A-56-41,816).
Improved reaction conditions for the vapor phase oxidation of a C4 hydrocarbon by the use of a vanadium-phosphorus oxide catalyst have been also proposed (JP-A-61-191,680 and JP-A-61-251,678).
Further, methods for the production of vanadium-phosphorus oxides as a catalyst for the production of maleic anhydride have been inserted in numerous pieces of literature besides the patent publications mentioned above. They are described in detail in B. K. Hodnett, ed., Catalysis Today, Vol. 1, No. 5 (1987), for example.
The conventional vanadium-phosphorus oxide, when used as a catalyst for a vapor phase oxidation such as, for example, in the production of maleic anhydride, manifests such a catalytic activity as is generally insufficient and is particularly inefficient at relatively low temperatures. In producing maleic anhydride under commercially favorable conditions, therefore, this catalyst is inevitably at a disadvantage in affording maleic anhydride only in an unduly low yield. Since the conventional vanadium-phosphorus oxide catalyst is prone to variation of the valency of vanadium, the production of a vanadium-phosphorus oxide catalyst vested with expected catalytic properties depends on chances. The production under discussion, to be successfully commercialized, therefore, entails an extremely detrimental problem of leaving the yield of maleic anhydride wholly at the mercy of the variation among lots of catalyst.
An object of this invention, therefore, is to find a solution to the drawbacks of the conventional vanadium-phosphorus oxide catalyst as mentioned above and provide a novel vanadium-phosphorus oxide for the vapor phase oxidation.
A further object of this invention is to provide a novel vanadium-phosphorus oxide possessing a specific X-ray diffraction pattern and a method for the production thereof.
Another object of this invention is to provide a novel vanadium-phosphorus oxide which can be manufactured with high repeatability as to the catalytic performance.
Still another object of this invention is to provide a catalyst formed of the vanadium-phosphorus oxide and used for a vapor phase oxidation.
Yet another object of this invention is to provide a method for the partial vapor phase oxidation of a hydrocarbon.
A further object of this invention is to provide a method for the production of maleic anhydride by the partial vapor phase oxidation of a hydrocarbon of four carbon atoms.